Automatic signal for trunk-lines of telephone-exchanges



(No Model.)

0. A. BELL. AUTOMATIC SIGNAL FOR TRUNK LINE-SOP TELEPHONE EXCHANGES.

No. 507,988. Pater ted Nov. 7, 1893.

INVENTOH Ora A Bel Z ,BJ dm f WITNES S w 002 WA$MINGTON D O UNITEDSTATES PATENT OFFICE.

ORO A. BELL, OF BROOKLYN, NEW YORK, ASSIGNOR TO THE WESTERN ELECTRICCOMPANY, OF CHICAGO, ILLINOIS.

AUTOMATIC SIGNAL FOR TRUNK-LINES F TELEPHONE-EXCHANGES.

SPECIFICATION forming part of Letters Patent No. 507,983, dated November'7, 1893.

Application filed February '7, 1893. Serial No. 461,315. (No model.)

Telephone exchange systems frequently comprise a number of exchangeoffices, to

each of which a large number of telephone lines are connected. Eachexchange office is provided with switching apparatus by whichconnections may be made between the difierent telephone lines connectedwith it, and the different offices are connected with each other by linecircuits, by means of which any telephone line terminating at one officemay be connectedto a line terminating in any other office of the system.These circuits extending between the different exchange offices of theexchange system are termed trunk lines. When a subscriber, whose lineterminates at one exchange office, desires a connection with thesubscriber whose line terminates at another office, the callingsubscriber may send his signal to his own oftice in the usual manner;the operator thereat, who receives the signal, having received the orderfor connection, will connect the subscribers line with a trunk lineextending to the exchange office at which terminates the line with whichconnection is desired, and will signal the operator at that office. Whenthis operator has responded, the first operator will communicate theorder to the second operator, who will thereupon establish connectionbetween the trunk line and the line called for. Thus the subscribersstations are connected together in a circuit including their respectivelines, the connecting apparatus at the two exchange offices, and thetrunk line extending'between the two offices.

Heretofore it has been customary to provide lines and telephonicappliances by which an operator at one ofli'ce might give the orderorally to the operator at another oflice to connect a particular trunkline with some particular subscriber at the second office. When thesubscribers had finished their conversation and signaled fordisconnection, such signal has ordinarily been received by appropriateapparatus at the office of the operator who first received the call; andapparatus is arranged so that the act of disconnecting the trunk linefrom the telephone line at that office automatically transmitted asignal to the operator at the other office. Upon receiving the automaticsignal, the operator at the sec- 6 5 0nd office proceeded to disconnectthe trunk line from the subscribers line at her switchboard.

My invention particularly relates to apparatus for transmitting suchautomatic signals for disconnection over trunk lines of exchangesystems; its object is to provide improved apparatus therefor, and toadapt the same to the exchange systems in general use.

The systems heretofore in use have required 7 5 two or more conductorsin addition to the conductors of the trunk line circuit. This is notdesirable on trunk'lines of any considerable length, since such trunklines commonly extend through cables, and the existence of anyunnecessary wire reduces the efficiency and desirability of the system.

In my invention I employ but two conductors for the automaticdisconnection circuit; one of these conductors may be one of the trunkline wires, and the return circuit may be through the earth. In myinvention I provide a springjack and mechanism in connection therewithby which the said signal circuit is normally closed'at the sendingoffice, but is opened thereat by the insertion of a connecting plug intothe springjack; and other mechanism at the receiving station retainingthesignaling circuit normally open thereat, but adapted to be operatedin the act 5 of making connection with the trunk line to I close thesame. An annunciator, or any suitable indicator, is located at thereceiving end of the trunk line, included in the signaling circuit, anda source of electricity is also intoo eluded therein.

, In practice the trunk line may terminate in a springjack located uponthe switchboard at the sending office, or, when the switchboard is ofthe multiple type, in several springjacks connected in paralleltherewith, located upon the different sections of the switchboard; andat the receiving end the trunk line may terminate in a terminal plugadapted for insertion into any springjack, and normally resting in asocket provided with a cord switch.

I preferably employ springjacks comprising, in addition to the linesprings, contact pieces adapted to be crossed together by the insertionof a plug into the jack. These contact pieces form the normallyseparated terminals of a local circuit including a battery and the coilsof a relay whose contact points are arranged to open the signalingcircuit, as described, when its coils are energized. Thus, when anoperator desiring to use a trunk line,.inser ts a connecting plug into aspringjack of that trunk line, she closes the normally open localcircuit, whereby the relay is actuated to separate its contact pointsand open the signaling circuit, as described. The cord switch at thereceiving end may have contact points which are normally separated fromeach other, but which are closed together when the'plug is removed fromits socket, These contactpoints are included in the,;s ignaling circuit;Thus as long as no connecting plug is present in any springjack of thetrunk line at the sending end, the signaling circuitis normally closedthereat; and aslOngas the terminal plug of the trunk lineat thereceiving end is not in use, the signaling circuit is open thereat;butin making use of a trunk line, the signaling circuit is opened at thesending oflice when connection is made to the trunk line; and is closedat the receiving end as soon as the operator there'at, havingreceivedthe order to connect the trunk line with some subscriber connect ed withher ofiice, has lifted theterminal plug of the trunk line from itssocket to make the desired connection; whereby the indicator orannunciator at the receiving end remains inert as long as the trunk lineis idle, and, also while it is in use in a complete connection; but whenthe operator at the, sending otfice, has received the signal todisconnect the two subscribers, and accordingly removes theconnectingplug from the springjack of the trunk line, the signaling circuit isclosed and, the annunciator or indicator at the receiving end isoperated and notifies the receiving operator that she may remove theconnection from the trunk line.

In some cases I have employed a second relay-in place of the annunciatorat the receiving end of the signaling circuit, and have arranged therelay contacts to close a local circuit including a suitable indicator.

I have illustrated my invention in theaccompanying drawings, Figures 1and 2.

In Fig. 1 of the drawings I have shown a trunk line equipped withapparatus such as tact springsd and d I have described, extendingbetween two exchange otlices. Fig. 2 represents two subscribers stationsconnected by lines with the usual appliances and apparatus at twodifferent exchange offices, a trunk line connecting the two exchangeolfices, and the operators connecting appliances at the station at whichthe call was received, in position of connecting the calling snbscribersline with the trunk line.

Referring to Fig. 1, A and B are supposed to be the different exchangeoflices, A being the office from which connections to subscribers ofoiiice B are made. The dilterent sides a c of the trunk line circuit,extending between the oifices A and B, are connected with the linesprings d and the thimbles df, re spectively, of two springjacks e e, ofwell known pat-tern, supposed to be located upon the two difierentsections of a multiple switchboard. The springjacks e and e have, in addition to their line contacts at at, other con- The contact springs d dof the different springjacks constitute the normally separated terminalsofa local circuit which includes a batteryf and the coils of a relay 7.The contact points h h of the relay control the continuity of a branch11 extending from one side 0 of the trunk line circuit to earth, andincluding a battery 7c. The springjacks shown are of well knownconstruction and are employed in connection with it a loop plug having,in addition to the tip and sleeve which make contact with the linespring and the thimble, respectively, of the jack, an

insulated conducting ring which crosses together the local contacts 6101 At the receiving station the lines cc terminate in the plug 1. Thisplug rests normallyin a socket,atone side of which is located the cordswitch m. This switch comprises the spring m, which bears against thesideot' the plug when the latterisin the socket, and two lighter springs'm m which tend to separate from each other. While the plug is in itssocket, the spring m is pressed outward and allows the springs m m toseparate, but when the plug is removed from its socket, the spring mmoves inward, and,

through the medium of the insulating stud m presses the spring m againstspring in, and thus places them in electrical connection. The spring mis connected with theside c of the trunk line circuit. The spring m isconnected to earth through a branch which includes the coils of a relayn, whose contact points 01' n control a local circuit including theindicator 0. This indicator may be any suitable device adapted to bedisplaced or caused to give an indication while current traverses it,and to return to its normalposition when it is de-energized--such, forexample, as a galvanometer. In connection with the trunk line circuits 0c is shown a telephone circuitp 1) connected with a telephone set ateach of the stations A and B. This is to enable the operatorat thesending station A to transmit the order for the desired lIO who isassumed. to.be continually listening at the'telephone q. An ordinarysignaling circuit may, of course, be employed in place of the telephonecircuit, or in connection with the trunk line itself; all theseappliances are well known in the art, and form no part of my inventionherein. 7

Referring now to Fig. 2, I will describe in detail the apparatus showntherein, and will trace the operation of establishing connec tionbetween the two substations shown, by means of the trunk line and otherappliances, and will point out the use of my invention in connectiontherewith. The substations 1 and 2 are supposed to be equipped withtelephonic and signaling appliances of the usual character. They areconnected by line circuits r and r, respectively, each with a springjackr and an annunciator r upon a switchboard at one of theoflices-substation 1 being connected with the oflice A, and substation 2with oflice B. The operator at office Ais provided with connectingplugs, and telephonic and calling apparatus of perfectly well known formand arrangement. The difierent portions of the two connecting plugs areelectrically connected together, a ringing key being included in thecircuit of the conductors connecting them, adapted to disconnect one ofthe plugs from the other and to connect it to the two poles of a callinggenerator. A telephone set 5 is provided for the operator, connectedwith a key t, by which she is enabled to connect her telephonealternately to the connecting plug circuit and to the telephone line 10p. A clearing-out annunciator u is permanently connected with the plugcircuit.

In the operation of the system shown, if the subscriber at station 1should desire connection with subscriber at station 2, he would send theusual calling signal to-the exchange office A in the usual manner, byrotating his calling generator. having charge of the annunciator of theparticular line to station 1, seeing the annunciator r operated, willinsert one plug c of a pair into the springjack r of the line signaling,and will place her keyt in position to connect her telephone set withthe plug 1). She is thus enabled to receive the order of subscriber atstation 1 for the connection desired. Recognizing that the stationcalled for is connected with a different exchange office, namely, officeB, the operator at office A addresses the operator at office B by meansof the talking or telephonic circuit'p p, and gives an order for theoperator at station E to establish connection between the trunk line 0 cand the subscribers line to station 2. The operator at office A theninserts the remaining plug *0 of the same. pair of plugs into thespringjack eof the trunk line, whereby the subscribers line circuitfromstation 1 is continued through the contact points of The operatorthe springjackr to the like contacts of the plug 1), and thence to thesimilar contacts of the plug 4;, thence to the corresponding conductorsc and c of the trunk circuit, and thence to the terminal plug 4. By theactof inserting the plug 1) into the springjack e,

the automatic signaling circuit of the trunk line was opened at thatspringjack. The operator at office B now, complying with the order whichshe received, inserts the terminal plugl into the springj ack r of lineto station '2 at her switchboard, whereby the line circuit is continuedto station 2. The operator at office B maynotify the operator at officeA that the connection has been completed, and the operator at office Amay, by depressing her calling key, send a signaling current tosubstation 2. When the subscriber thereat has responded and has removedhis telephone from its switch-hook, the circuits are in position toallow of communication between the subscribers. lVheu they havecompleted their conversation, either of them may rotate his callinggenerator andsend a signaling current upon the line circuit. Thissignaling current will find circuit through the clearing-outannunciatoru at the office A, and will operate the same, thus indicatingto the operator at that switchboard that the connection is no longerdesired. That operator then removes the connecting plugs o o from thespringjacks into which they are inserted. This act allows the relay 9 tobecome de-energized, when its contact points close together and completethe earth branch t' containing 4 the battery 70; the'automatic signalingcircuit is thereby completed, being already closed at the contact pointsm m ofthe cord switch and the relay n is operated, closes its contactpoints, and thus actuates the indicator 0.

The operator at office B is thus informed that the connection betweenthe line to station 1 and the trunk line has been removed, and sheremoves the terminal plug Z from the spring jack of line to station 2and returns it to its socket. The cord switch is: thus operated to openits contact points, and the indicator 0 returns to its normal position.v

Having thus described my invention, I claim as new and desire to secureby Letters Patent- 1. The combination with a trunk line, of'a signalingcircuit including a source of electricity, contact points at one of theoffices included in the signaling circuit adapted to be separated by theact of connecting with the trunk line, contact points included in thesignaling circuit at the other station adapted to be closed together bythe act of making connection with the trunk line thereat, and anindicator in the signaling circuit at said second office, whereby saidindicator is operated by the removal of the connection at the firstoffice when connection ekists from the trunk line at the second office,substantially as described.

2. The combination witlratrunk line, of a signaling eirciiit including aportion of the trunk line, contact points at oneend of said trunk lineadaptedto bese'parated whemconne'ction ismade to the trunk line at thatend,

cc'ntact points at the other end of the trunk line adapted to'beclosedwhen co'nnectien "is made to'thet endof the trunk line, saidcontact pdilits beifigiticluded in-the'si'gnaling circiiit, "and'anindicator cchnectedwith the signaling circuit-substantially asdescribed.

" 3. In 'cbtnbination with-a ti'u'n'kdine extendin "saidsignmingeircuitga socket and cord the terminal pl'ug is but "ofthe-socket, a seifrce bf elet'fieity' i'n" thesign alinghircliit,"

1 of electricity included in thecircui'c' formed office included in saidcircuit, "slibstaht-ially 1 asdes'cribed.

In "witness whereof "I hereunto subscribe *hiy liifne this 10th day-ofDecerriben-A. D. I892.

0R0 A. =BELL.

'Witnesses:

